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3) With a headwind, a plane traveled 840 miles northward in 2 hours. With the same wind as a tail wind, the return trip took 1 hour and 45 mineutes. Find the plane's airspeed and the wind speed.

 

 for 3), I attempted this problem by simply making a graph... I got confused...

 

4) With a tailwind, a small plane traveled 420 miles in one hour and 30 min. The return trip took 30 min longer. Find the wind speed and airspeed of the plane...

 for 4) I plugged in random numbers for both... I think I made the wrong equation... PLS HALP

 Jun 25, 2019
 #1
avatar+18439 
+2

 Rate x time = distance

 

Rate = Speed + wind    or speed - wind

 

speed-wind    *  2   = 840

 

Speed + wind  * 1.45 = 840          Two equations    with    two unknowns  

 

From first equation   W+420 =S      Sub in to the second equation

 

(W+420+W)*1.45 = 840

W= 30 mph

 

Sub this result in to one of the equations to solve for  S

S-30       * 2 =  840         S = 450  mph

 Jun 26, 2019
 #2
avatar
0

EP: How did you get: 

(W+420+W)*1.45 = 840

W= 30 mph ???

1 hour and 45 minutes =1 hour + 45/60 =1.75 -An hour and three-quarters. Why did you multiply by 1.45 ???.

Your W works out =2310 /29 =~79.65 ???

 Jun 26, 2019
 #7
avatar+18439 
+1

That was just a typo    1.45 should be 1.75     or  1:45      answer does not change....when I calculated it I used 1.75   but I typed 1.45

ElectricPavlov  Jun 26, 2019
edited by ElectricPavlov  Jun 26, 2019
 #3
avatar+28064 
+3

Perhaps the following will make it clearer:

 

EP made the trivial mistake of setting 1 hour 45 mins (i.e. one and three quarter hours) as 1.45 hours rather than 1.75 hours

 

Now see how you get on with your question 4) . 

 Jun 26, 2019
 #4
avatar+101813 
+1

3) With a headwind, a plane traveled 840 miles northward in 2 hours. With the same wind as a tail wind, the return trip took 1 hour and 45 mineutes. Find the plane's airspeed and the wind speed.

 

Note....1hr 45 min  =  1.75 hrs

 

Let the speed of the plane in still air be S

Let the wind speed  be W

 

Against the wind the plane's rate is  (R - W)  ....the wind slows the plane's normal speed

With the wind the plane's rate is (R + W).....the wind increases the plane's normal speed

 

So.....  Rate * Time  =  Distance   and we have that

 

(R -W) * 2  =  840   ⇒  2R - 2W  =  840  ⇒   R - W  = 420  ⇒   R  = 420 + W    (1)

(R + W) *1.75  = 840  ⇒  1.75 R + 1.75W  = 840    (2)

 

Sub (1)  into (2)   for R  and we have that

1.75(420 + W) + 1.75W  = 840

735 + 1.75W + 1.75W  = 840

735 + 3.5W  = 840       subtract 735 from both sides

3.5W  =  105       divide both sides by  3.5

W  = 30  mph = wind speed

 

And using (1) the plane's speed  is  420 + 30  =  450 mph

 

 

cool cool cool

 Jun 26, 2019
 #5
avatar+101813 
+1

 

4) With a tailwind, a small plane traveled 420 miles in one hour and 30 min. The return trip took 30 min longer. Find the wind speed and airspeed of the plane...

 

This one is similar to (3)

 

1hr 30 min  = 1.5 hrs.....so

 

(R + W) * 1.5  =  420     (1)

(R-W )  *2  =   420    ⇒ 2R - 2W  = 420   ⇒  R - W  = 210  ⇒  R  = 210 + W   (2)

 

Sub (2) into (1)   for R  and we have that

 

(210 + W + W) * 1.5   = 420

(210 + 2W) * 1.5  =  420

315 + 3W  =  420     subtract   315 from each side

3W  =  105        divide both sides by 3

W  = 35   mph

 

And using (1) ,  R  =  210 + 35  =  245 mph

 

 

cool cool cool

 Jun 26, 2019
 #6
avatar+625 
+4

Wow CPHILL.. Great job!

tommarvoloriddle  Jun 26, 2019

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